1. Field of the Invention
The present invention pertains to the endovascular treatment of aneurysms and the like, using embolic coils, and more particularly, pertains to the endovascular placement of such coils using introducer catheters.
2. Description of the Related Art
The endovascular treatment of a variety of lesions throughout the body has become an increasingly popular method of therapy. For example, introducer catheters have been used to place remedial devices and materials such as balloons, coils, particles, adhesive and alcohol to target lesions. One particular example is the treatment of an aneurysm by placing radiopaque materials within an aneurysm pouch. For example, it is known to push embolic coils through an introducer catheter, having a free end positioned at the desired deposition site. However, once the embolic coils leave the introducer catheter they are no longer under control and may become repositioned away from the desired location. This might occur, for example, when the treatment site is located near a vessel having a larger lumen, as when the embolic coil, having migrated to the larger vessel, would travel to a remote location.
Another example of coil placement is given in U.S. Pat. No. 4,512,338. The coils used are of shape memory alloy, becoming enlarged when warmed by the body within which they are placed. The coils are passed through an introducer catheter, the free end of which is located at the desired treatment site. The introducer catheter is preferably thermally insulated to prevent premature expansion of the treatment coil. When the coil is pushed mechanically past the free end of the catheter, it is exposed to the warmer bodily tissue and bodily fluids at the treatment site. Auxiliary heating sources, either relied upon as a sole source of heat, or used in conjunction with the body heat associated with the deposition site, could also be employed. For example, infrared radiation could be employed to progressively heat and reform the shape memory alloy wire.
Another example of intravascular catheter treatment is given in U.S. Pat. No. 4,735,201, and in a related article entitled "Laser-Induced Thermal Occlusion of Berry Aneurysms: Initial Experimental Results", by Gerald V. O'Riley, Patentee of U.S. Pat. No. 4,735,201, Mark D. Forrest, William C. Schoene and Richard H. Clarke, Radiology, 1989, Vol. 171, pp. 471-474. Disclosed is an intravascular laser-catheter technique for intracranial aneurysms, suitable for use at the time of diagnostic angiography. A fiber optic probe is inserted through an introducer catheter, the free end of which is located adjacent the treatment site. The catheter axis is located generally normal to the treatment site, for example, at the base of a vascular T-junction.
A metal cap having the configuration of a paraboloid, or the like rounded tip, is pushed through the introducer catheter by a fiber optic probe. A recess formed in the metal cap receives the free end of the fiber optic and hot melt adhesive is located in the recess to secure the metal cap to the free end of the optic fiber. The optic fiber is secured directly to the metal cap with hot melt adhesive.
The optic fiber is employed to push the metal cap through the introducer catheter into position with respect to the desired treatment site. A laser light source located at the proximal end of the optic fiber discharges laser energy through the optic fiber at two different levels. The optic fiber is advanced until the metal cap presses against the site to be repaired, and a relatively high level of laser radiation is transmitted through the optic fiber to heat the metal cap to the extent that it causes coagulation of the tissue surrounding the neck of the aneurysm. The metal cap is dimensioned larger than the neck of the aneurysm, with the optic fiber developing pressure against the metal cap during coagulation.
Heating of the metal cap to cause coagulation softens the hot melt glue, and if tension were applied to the optic fiber, the distal or free end thereof might become dislocated from the metal cap. After the metal cap is allowed to cool and a bond established with the tissue at the neck of the aneurysm, a second burst of laser energy is transmitted through the optic fiber, sufficient to soften the hot melt glue, and to facilitate withdrawal of the optic fiber end therefrom. The second laser burst, for removal of the optic fiber, is at a lower energy level than the burst for producing coagulation.
U.S. Pat. No. 4,795,458 teaches a stent made of shape memory alloy in either tape or wire form for vascular implantation to prevent restenosis after balloon angioplasty. The coil has a diameter less than that of the blood vessel in which it is to be implanted, and grows or swells when heated to maintain the blood vessel lumen. The coil is pushed through an introducer catheter to a repair site. Hot saline solution is then past through the catheter into the bore of the wire coil, heating the coil sufficient to cause a shape change (enlargement). However, as with the aforementioned coils, control over the coil is lost once the coil passes through the free end of the introducer catheter.
It is desirable in many applications to retain control over the coil position and to facilitate retraction of the coil during positioning, if necessary. U.S. Pat. No. 4,503,569 employs a coil of shape memory alloy which is transluminally positioned to serve as a prosthesis for an endovascular graft. A hot saline solution, passed through the introducer catheter, heats the coil to its transition temperature causing expansion of the coil. As with the coils previously mentioned, retraction is not possible as positioning of the coil is accomplished solely by pushing the coil through the introducer catheter. Thus, considerable care must be exercised to prevent over-extension of the catheter or probe during coil placement.
U.S. Pat. No. 3,868,956 discloses an expandable appliance such as coil of shape memory alloy, which is expandable when heated. The appliance is pushed through an introducer catheter. A pair of electrical conductors are attached to the expandable appliance and remain attached thereto when the appliance is delivered to the treatment site. A current is then passed through the electrical conductors to cause heating of the appliance. As the introducer catheter is withdrawn from the appliance, the electrical conductors are separated therefrom and are withdrawn from the body.
In addition to the techniques described above, directed to the endovascular or transluminal deposition of a repair appliance, various balloon embolization therapies have been developed. For example, a treatment is described in the article entitled "Giant Cavernous Aneurysm Associated With Trigeminal Artery: Treatment By Detachable Balloon", Higashida et al., American Journal of Neuroradiology, 1981, Vol. 2, pp. 167-173. A related technique is reported in another article of the American Journal of Neuroradiology, entitled "Giant Unclippable Aneurysms: Treatment Detachable Balloons", by Debrun et al., Vol. 2., pp. 167-173, March/April 1981. These are examples of endovascular therapy of aneurysms, typically performed in patients with aneurysms that are surgically inaccessible. Two additional examples of balloon techniques are given in an article entitled "Intravascular Balloon Embolization of a Carotid-Opthalmic Artery Aneurysm With Preservation of the Parent Vessel", by Hieshima et al., American Journal of Neuroradiology, Vol. 7, pp. 916-918, September/October 1986; and an article by Higashida et al., "Cavernous Carotid Artery Aneurysm Associated With Marfan's Syndrome: Treatment By Balloon Embolization Therapy", Neurosurgery 1988, Vol. 22, No. 2, pp. 297-300. As an alternative to gas-filled balloons, U.S. Pat. No. 4,793,350 discloses a low profile dilatation catheter which eliminates the use of gas.
U.S. Pat. No. 4,425,908 discloses a blood clot filter of open wire, expandable configuration which is pushed through an introducer catheter and allowed to expand within a blood vessel. The expandable wire filter is passed through the catheter with a guide wire feeder device. U.S. Pat. No. 4,300,244 discloses a cardiovascular graft using a carbon-coated tightly wound spring to provide a biocompatible interior surface which provides an unobstructed passageway for blood flow. The arrangement provides a vascular prosthesis that can be readily installed in a relatively simple procedure.
Despite the above advances, several improvements are still being sought. For example, it is important in an endovascular procedure that the repair device be accurately positioned, to obtain maximum effectiveness. For example, in the treatment of aneurysms with embolic coils, it is important that the coils be accurately positioned with respect to the aneurysm pouch. At times, this requires not only extension, but also retraction of the embolic coil within the blood vessel.